Re: Re: Two questions about modification of a matrix.
- To: mathgroup at smc.vnet.net
- Subject: [mg101096] Re: [mg101057] Re: [mg101041] Two questions about modification of a matrix.
- From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
- Date: Wed, 24 Jun 2009 06:29:40 -0400 (EDT)
- References: <200906220822.EAA09140@smc.vnet.net> <200906231103.HAA07999@smc.vnet.net>
On 23 Jun 2009, at 20:03, Leonid Shifrin wrote:
>
> For the second problem, probably the easiest way to speed up code in
> case
> of large matrices is to use Compile:
>
> nullifyNegativeCompiled =
> Compile[{{matr, _Real, 2}},
> Module[{i = 1, j = 1, new = matr},
> For[i = 1, i <= Length[matr], i++,
> For[j = 1, j <= Length[matr], j++,
> If[matr[[i, j]] < 0, new[[i, j]] = 0]]];
> new]];
>
> My benchmarks indicate 3-fold speed - up on <largeTestMatr>, with
> respect to
> a rule-based solution.
In my tests the following is both simpler and much faster :
ClipNullify[mat_] := Clip[#, {0, Infinity}] & /@ mat
For example:
mat = RandomInteger[{-100, 100}, {1000, 1000}];
(m1 = nullifyNegativeCompiled[mat]); // Timing
{0.320822, Null}
(m2 = ClipNullify[mat]); // Timing
{0.013523, Null}
m1 == m2
True
Andrzej Kozlowski
- References:
- Two questions about modification of a matrix.
- From: Mayasky <alix.zhang@gmail.com>
- Re: Two questions about modification of a matrix.
- From: Leonid Shifrin <lshifr@gmail.com>
- Two questions about modification of a matrix.